Chaotic Psychoplasm

Pure chaos flesh barely contained by our feeble laws of physics. Surface appears as liquid skin, so eyes, mouths, teeth, hair, fingernails, nipples, and genitalia all swim across its surface. Its interior "biology" is similarly amorphous. It is mindless, incredibly aggressive, and has no control over its abilities.

I love that this gibbering mouther is apparently scaring itself

d4 Bodytype/Movement (roll once when players first encounter it)

Levitation (as human)

Spider legs (as horse)

Membranous wings (as pterodactyl)

Immobile (attached to floor/wall, can teleport 100' each round)

d10 Noises That It Makes Continuously (roll at beginning of combat, and again when bloodied)

Evil clone of a PC with weirdly organic copy of all equipment. It's actually an evil midget version, so it has half HP but is otherwise identical. Clone and gear will melt into a bloody goo after 1d6 rounds, screaming curses and praising Cthulhu.

2d6 hairless, legless wolves. Use wolf stats except that they slither like snakes (half speed) and have -2 to AC.

Doubles in size. Double current HP. This can only happen once (reroll otherwise).

Major Illusion. Upper half of the dungeon is ripped away, exposing the stars of an alien sky. Above, a vast thing that vaguely resembles a mosquito's face regards the combat dispassionately. Cold wind blows through battleground, dealing 1d4 cold damage each round to those who failed their save vs. illusion. Blood leaks from everyone's eyes. Lasts until the end of combat. This can only happen once (reroll otherwise).